The ability of users to access programs and share data over local area networks (referred to as “LANs”) has become a necessity for most working environments. To improve efficiency and ease of use, certain enhancements such as mobile wireless access may be added to transform a LAN into a wireless LAN (WLAN). Commonly, WLANs are adapted to support wireless communications in accordance with the current Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard. Herein, the “current IEEE 802.11 standard” represents the original 802.11 standard developed in 1997 as well as any or all enhancement standards already ratified (e.g., IEEE 802.11a/b/g/d/h/i).
For instance, in accordance with the current IEEE 802.11 communication standard, a wireless mobile device conducts a scanning process before it associates, namely establishes an Open Systems Interconnection (OSI) Layer 2 wireless link, with an access point (AP). This scanning may be conducted actively or passively through the detection of beacons for example. The scanning process is conducted quite frequently, typically when the mobile device needs to establish or re-establish communications with an AP in response to an event such as a power-down, dropout, or even general roaming where the mobile device needs to move from one AP to another AP. At this time, the mobile device conducts a scanning process in order to identify available candidate APs and to receive information concerning these APs. Based on this information and some local policies, the mobile device will select one AP and try to associate with the selected AP.
More specifically, in accordance with the current IEEE 802.11 standard, the conventional active scanning process involves the mobile device switching to a first channel (Channel 1), sending a PROBE REQUEST message and waiting for PROBE RESPONSE messages from neighboring APs. Thereafter, the mobile device switches to a second channel (Channel 2), sends another PROBE REQUEST message and waits for PROBE RESPONSE messages. The mobile device repeats the process until all of the channels have been scanned. For current IEEE 802.11b communications operating in the North American allocated frequency band, eleven (11) channels are scanned while current IEEE 802.11a communications involve twenty (20) channels.
Clearly, the active scanning process for multi-mode deployment communication schemes (e.g., IEEE 802.11a/b/g) is quite time consuming, which adversely affects network performance during roaming. In fact, for many WLAN applications including Voice-Over-Internet Protocol (VoIP) requiring a fifty-millisecond (50 ms) or faster transition time, the current scanning delay is not acceptable. As a result, there is continued interest to optimize the scanning process by minimizing scanning delays.
There have been attempts to optimize the scanning process, such as conducting an initial scanning of the most popular channels. For example, when supporting current IEEE 802.11b, the optimized scanning process for the mobile device would begin by scanning Channel 1, then scanning Channel 6 followed by Channel 11. The reason is that Channels 1, 6 and 11 are the most popular since they are fully non-overlapping. However, this optimized scanning process fails to provide a more efficient scanning process for all wireless networks, especially when Channels other than 1, 6 and/or 11 are in use.